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Make endian_reverse constexpr when possible

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This commit is contained in:
Peter Dimov
2019-10-11 19:43:02 +03:00
parent 3c296ff707
commit a4bc0f1a44
2 changed files with 21 additions and 5 deletions
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22
include/boost/endian/detail/endian_reverse.hpp
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@ -16,6 +16,20 @@
#include <cstddef> #include <cstddef>
#include <cstring> #include <cstring>
#if defined(BOOST_ENDIAN_NO_INTRINSICS)
# if defined(BOOST_NO_CXX14_CONSTEXPR)
# define BOOST_ENDIAN_CONSTEXPR
# else
# define BOOST_ENDIAN_CONSTEXPR constexpr
# endif
#else
# if defined(BOOST_ENDIAN_CONSTEXPR_INTRINSICS)
# define BOOST_ENDIAN_CONSTEXPR BOOST_CONSTEXPR
# else
# define BOOST_ENDIAN_CONSTEXPR
# endif
#endif
namespace boost namespace boost
{ {
namespace endian namespace endian
@ -30,12 +44,12 @@ namespace detail
// -- intrinsic approach suggested by reviewers, and by David Stone, who provided // -- intrinsic approach suggested by reviewers, and by David Stone, who provided
// his Boost licensed macro implementation (detail/intrinsic.hpp) // his Boost licensed macro implementation (detail/intrinsic.hpp)
inline uint8_t endian_reverse_impl( uint8_t x ) BOOST_NOEXCEPT inline uint8_t BOOST_CONSTEXPR endian_reverse_impl( uint8_t x ) BOOST_NOEXCEPT
{ {
return x; return x;
} }
inline uint16_t endian_reverse_impl( uint16_t x ) BOOST_NOEXCEPT inline uint16_t BOOST_ENDIAN_CONSTEXPR endian_reverse_impl( uint16_t x ) BOOST_NOEXCEPT
{ {
#ifdef BOOST_ENDIAN_NO_INTRINSICS #ifdef BOOST_ENDIAN_NO_INTRINSICS
@ -48,7 +62,7 @@ inline uint16_t endian_reverse_impl( uint16_t x ) BOOST_NOEXCEPT
#endif #endif
} }
inline uint32_t endian_reverse_impl(uint32_t x) BOOST_NOEXCEPT inline uint32_t BOOST_ENDIAN_CONSTEXPR endian_reverse_impl(uint32_t x) BOOST_NOEXCEPT
{ {
#ifdef BOOST_ENDIAN_NO_INTRINSICS #ifdef BOOST_ENDIAN_NO_INTRINSICS
@ -62,7 +76,7 @@ inline uint32_t endian_reverse_impl(uint32_t x) BOOST_NOEXCEPT
#endif #endif
} }
inline uint64_t endian_reverse_impl(uint64_t x) BOOST_NOEXCEPT inline uint64_t BOOST_ENDIAN_CONSTEXPR endian_reverse_impl(uint64_t x) BOOST_NOEXCEPT
{ {
#ifdef BOOST_ENDIAN_NO_INTRINSICS #ifdef BOOST_ENDIAN_NO_INTRINSICS

4
include/boost/endian/detail/intrinsic.hpp
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@ -18,7 +18,7 @@
#define __has_builtin(x) 0 // Compatibility with non-clang compilers #define __has_builtin(x) 0 // Compatibility with non-clang compilers
#endif #endif
#if defined(_MSC_VER) #if defined(_MSC_VER) && ( !defined(__clang__) || defined(__c2__) )
// Microsoft documents these as being compatible since Windows 95 and specifically // Microsoft documents these as being compatible since Windows 95 and specifically
// lists runtime library support since Visual Studio 2003 (aka 7.1). // lists runtime library support since Visual Studio 2003 (aka 7.1).
// Clang/c2 uses the Microsoft rather than GCC intrinsics, so we check for // Clang/c2 uses the Microsoft rather than GCC intrinsics, so we check for
@ -46,6 +46,8 @@
# define BOOST_ENDIAN_INTRINSIC_BYTE_SWAP_4(x) __builtin_bswap32(x) # define BOOST_ENDIAN_INTRINSIC_BYTE_SWAP_4(x) __builtin_bswap32(x)
# define BOOST_ENDIAN_INTRINSIC_BYTE_SWAP_8(x) __builtin_bswap64(x) # define BOOST_ENDIAN_INTRINSIC_BYTE_SWAP_8(x) __builtin_bswap64(x)
# define BOOST_ENDIAN_CONSTEXPR_INTRINSICS
// Linux systems provide the byteswap.h header, with // Linux systems provide the byteswap.h header, with
#elif defined(__linux__) #elif defined(__linux__)
// don't check for obsolete forms defined(linux) and defined(__linux) on the theory that // don't check for obsolete forms defined(linux) and defined(__linux) on the theory that